[P4–427]: EFFECT OF ISOFLURANE ON NEUROPATHOLOGY AND COGNITIVE IMPAIRMENT IN THE TRIPLE TRANSGENIC ALZHEIMER's MOUSE MODEL

oligomerization. Methods: We have generated tools to constrain dimerization of APP CTFs and force specific orientations of such CTF dimers. By replacing the APP extracellular domain with a dimeric coiled coil (Put3) downstream of an HA tag, we engineered TM APPC99 fusion proteins (cc-C99) in which the helical TM domains are constrained into seven possible relative orientations as left-handed coiled coils. These dimers can individually be tested for signaling/ gene induction and amyloidogenic processing by monitoring Ab and AICD generation. This approach has successfully been used for identifying the active conformation of EPO and TPO receptor dimers. Results:We show that a particular orientation of APP TM dimers (cc-C99 del6) favors its processing by the g-secretase, and the formation of stable assemblies that appear to be “Ab-like” oligomers, as they lack the C99 N-terminus. Another orientation of APP TM dimers (cc-C99 del7) is an active conformation in intracellular signaling and strongly induces APP-dependent gene transcription. Both orientations contain Gly residues in the TM dimer interface, but the Gly residues belong to successive Gly-xxx-Gly residues in the motifs. Molecular modeling indicates that a switch Gly residues in the interface of C99 dimers might occur after AICD generation, leading to stabilization of a cc-C99 del6 orientation that favors amyloid generation and oligomerization. Conclusions:The precise dimeric TM orientation of C99 appears to play a major role in the processing by g-secretase for the release of Ab and AICD.